The 20-year-old entertainer took to Twitter after Seth appeared on Watch What Happens Live (via People) and called Justin a number of things, including “obnoxious,” “ungrateful,” “insincere,” and “a piece of sh-t.”

Justin just tweeted, “Seth Rogan sorry I didnt bow down when I asked 2 meet u was probably a bit shy and didn’t want to be over the top but still. love ur movies.”

This refers to the time Justin asked to meet Seth while both were on set of a German talk show.

“I was like, ‘Sure, I’ll meet him,’” Seth explained on The Howard Stern Show (via Billboard). “So I went outside to meet him and he was acting like I asked to meet HIM! It was very nonchalant, ‘Yo man. What’s up?’ and I was like, ‘What the f-ck, I don’t give a f-ck about, I don’t want to meet you. Don’t act all nonplussed to meet me. I didn’t want to meet you. I was totally cool not meeting you… But I was like, fine, I wouldn’t have said anything, I was like, ‘He’s a bit of a motherf-cker.’”

He added, “He’s a good example of someone you meet, who you think you’re going to hate, and then you get to hate him as much as you thought. You meet him, and he lives up to every one of your expectations of how you hope he will be.”